Ball joints usually are made up of a ball member and a bearing seat member. Such joints may also be referred to as universal joints since they allow movement around the joint in all directions, unlike joints which allow movement around an axis in only one plane, such as hinges.
The ball member of ball joints has a spherically-shaped bearing surface formed over at least a portion of its outer surface. The bearing surface may be formed over only a central portion of the ball member and one or more other portions may have non-spherical surfaces. One side of the ball member may be connected to a connecting arm, rod, stub or other elongated means for attaching the ball member to a frame member, an arm member, or other support member. The connector member may include a threaded end which facilitates attaching the connector member to the support member.
The bearing seat member has a bearing surface on its inner surface which is shaped to complement the bearing surface on the ball member so that these bearing surfaces are in sliding engagement with each other. The bearing seat member of a bearing assembly has a passage connecting the interior socket formed by its bearing surface with the outside of the member. When the ball member is engaged in the socket of the seat member, the connector member attached to the ball member extends through this passage and is connected to the frame of whatever apparatus the bearing assembly is being used with. The passage must be sufficiently wide to allow the seat member freedom of movement over the desired range, but not so large as to allow the ball member to fall out of the socket or to allow the seat member to travel over too great a range of movement.
Ball joints and bearing assemblies having a ball member are used in a variety of well known applications. For instance, trailer hitches for automobiles towing trailers usually include a ball member attached to an arm which is then fixed to the frame of the car, and a bearing seat member attached to a tongue extending from the trailer being towed. Ball joints are also an integral part of vehicle steering assemblies and suspension systems. For example, in steering systems, ball joints may be used to connect a tie rod to a rod end bearing on the arm of a steering knuckle. In vehicle suspension systems, ball joints may be used to connect an independent suspension between the vehicle and the wheel. Ball joints are also used in a variety of other applications.
While ball joints of the type described above are in use, the bearing surfaces on the ball member and the bearing seat member rub against each other. As the two bearing surfaces rub against each other, the bearing surfaces can be worn down through friction. As the bearing surfaces are worn down, the joint becomes loose and steering control can become sloppy. As a result, members of a steering assembly, for example, may move from their intended positions and therefore slack develops in the steering assembly.
As a result, the vehicle will more easily move away from the path the operator directs it on, the vehicle steering will become less precise and less predictable, and the vehicle therefore may become difficult to control. For example, 0.002 to 0.003 inch of slack in the ball joint of a vehicle steering assembly is sufficient to cause the vehicle to turn away from straight ahead. Obviously, a vehicle having a steering assembly in which such slack exists can make the vehicle difficult to control, and may even be dangerous. The problems caused by a loose joint can be especially bad if the vehicle is a large vehicle, such as a truck.
Slack in other ball joints can cause similar problems. For instance, where a ball joint is incorporated into a trailer hitch, a slack joint can cause the trailer to sway from side to side behind the towing vehicle. Such a situation can be very dangerous both to the person trying to control the vehicle and other motorists on the road. Similarly, a slack joint in a vehicle suspension system can adversely effect the safety of the vehicle, as well as the quality of the ride and the comfort of the occupants.
As evident from the above discussion, slack in ball joints can have serious consequences to the apparatuses in which the ball joints are incorporated, and to the users thereof. There is therefore a need for a slack free ball joint assembly.